JCECE Engineering JCECE Engineering Solved Paper-2009

  • question_answer
    Coefficient of \[{{x}^{n}}\] in the expansion of\[1+\frac{a+bx}{1!}+\frac{{{(a+bx)}^{2}}}{2!}+\frac{{{(a+bx)}^{3}}}{3!}+...\]is

    A) \[\frac{{{e}^{a}}{{b}^{n}}}{n!}\]                               

    B) \[\frac{{{(b\cdot a)}^{n}}}{n}\]

    C) \[\frac{{{e}^{b}}\cdot {{b}^{n}}}{(n-1)!}\]                            

    D) \[\frac{{{a}^{n}}\cdot {{b}^{n-1}}}{n!}\]

    Correct Answer: A

    Solution :

    We know, \[{{e}^{x}}=1+\frac{x}{1!}+\frac{{{x}^{2}}}{2!}+\frac{{{x}^{3}}}{3!}+...\] Put         \[x=(a+bx)\] \[\therefore \]  \[{{e}^{a+bx}}=1+\frac{a+bx}{1!}+\frac{{{(a+bx)}^{2}}}{2!}\]                                                 \[+\frac{{{(a+bx)}^{3}}}{3!}+...\] \[\therefore \] Coefficient of\[{{x}^{n}}\]in\[{{e}^{a+bx}}\]                 \[={{e}^{a}}\frac{{{(b)}^{n}}}{n!}\]


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